A circle with circumference $12\pi$ has an arc with a $40^\circ$ central angle. What is the length of the arc? ${12\pi}$ ${40^\circ}$ $\color{#DF0030}{\dfrac{4}{3}\pi}$
Explanation: The ratio between the arc's central angle $\theta$ and $360^\circ$ is equal to the ratio between the arc length $s$ and the circle's circumference $c$ $\dfrac{\theta}{360^\circ} = \dfrac{s}{c}$ $\dfrac{40^\circ}{360^\circ} = \dfrac{s}{12\pi}$ $\dfrac{1}{9} = \dfrac{s}{12\pi}$ $\dfrac{1}{9} \times 12\pi = s$ $\dfrac{4}{3}\pi = s$